【作者】 王勇强；

【导师】 侯建国；

【作者基本信息】 武汉大学 ， 结构工程， 2004， 硕士

【摘要】 部分预应力混凝土构件卸去部分荷载后具有良好的变形恢复性能。当卸去的荷载足够大时，最大使用荷载下已开展的裂缝可以很好地闭合。对于承受的可变荷载较大的部分预应力混凝土梁，允许在荷载效应标准组合下短暂开裂，且其裂缝宽度在允许裂缝宽度范围之内，而在荷载效应准永久组合下保持裂缝闭合状态，结构仍将具有良好的使用性能和耐久性。工程设计中，若能充分利用部分预应力混凝土的这一特性，将可以减小预应力筋的用量，收到节约锚具、降低造价、减小反拱的效果。 为将部分预应力混凝土梁的裂缝闭合性能应用于工程实际，国内外学者已经做了大量的卓有成效的研究工作，对裂缝的闭合过程有了较为深入的认识，并提出了基于各自的试验数据的裂缝闭合弯矩的计算公式。但是，由于研究方法及计算侧重点的不同，各学者提出的裂缝闭合弯矩的计算公式对各自的试验数据符合较好，而对其他学者的试验数据则符合性较差。因此，有必要提出一个统一的裂缝闭合弯矩的计算公式。另外，已有的研究工作大都只局限于对裂缝闭合机理的研究上，而没有考虑裂缝闭合性能的适用条件和应用范围，也没有提出相应的考虑裂缝闭合性能的裂缝控制设计方法，即已有的研究均没有讨论在什么情况下可以利用部分预应力混凝土梁的裂缝闭合性能以及如何利用裂缝闭合性能的问题。 针对以上问题，本文主要做了以下几个方面的工作：(1)在已有的试验资料和理论研究的基础上，对部分预应力混凝土梁的裂缝闭合性能进行了进一步的深入研究，并通过全过程分析程序重点研究了闭合应力的取值问题；(2)提出了与各学者的试验数据符合较好的统一的裂缝闭合弯矩的计算公式；(3)通过研究发现：对于有粘结及无粘结的部分预应力混凝土梁，当闭合应力分别取1N／mm~2及2N／mm~2时，裂缝闭合弯矩的计算值与实测值符合良好。因此，计算裂缝闭合弯矩时，对于有粘结和无粘结的部分预应力混凝土梁闭合应力可分别近似地取为1N／mm~2和2N／mm~2。(4)介绍了裂缝宽度的影响因素和主要计算方法，阐述了采用简单的名义拉应力法进行裂缝控制的优点；(5)通过钢筋锈蚀机理和已有的暴露性试验，研究了横向裂缝宽度对部分预应力混凝土梁耐久性的影响；(6)对裂缝闭合条件进行了研究，结合荷载情况提出了卸载系数的概念，并在此基础上提出了基于卸载系数的部分预应力混凝土梁考虑裂缝闭合性能的适用条件和应用范围；(7)在以上研究的基础上，提出了部分预应力混凝土梁考虑裂缝闭合性能并利用名义拉应力法进行裂缝控制的建议公式。 设计实例证明：利用裂缝闭合性能对部分预应力混凝土梁进行裂缝控制可取得较好的经济效益；采用本文提出的裂缝控制建议公式可以很好地将部分预应力混凝土梁的裂缝闭合性能应用于裂缝控制设计。而且计算简便、概念清晰，可供工程设计和混凝土结构设计规范今后修订时参考。更多还原

【Abstract】 Partially prestressed concrete beams have a good property of deformation-renew. When load is removed enough, the cracks expanded under the biggest service load can close well. To the partially prestressed concrete beams with larger variable load, they still have good normal service performance and durability, when they are allowed to crack in the allowed range momently under the load effect nominal combination and the cracks can close under the load effect quasi-permanent combination. In structure design, if this property is full used, it can help to decrease the dosage of the prestressing tendon, save anchorage device, reduce cost and minish invert arch.In order to apply the crack-closing property of partially prestressed concrete beams to engineering practice, scholars at home and abroad have done a large amount of research work fruitfully. They have got a deep cognition to the course of crack closing and have put forward the empirical formulas respectively. However, their formulas fit well to the test data own to themselves but perforce bad to the others. So it’s essential to bring forward a uniform formulas to calculate the crack closing moment. In addition, the previous research work mostly focus on the crack closing mechanism, but neither the applicable conditions and ranges was considered nor the design methods of crack control that considering the crack-closing property was given. In other words, the previous study didn’t discuss when and how to make use of the crack-closing property.Aim at hereinbefore problems, the primary work are done: (1) Based on the previous test data and theory study, further research is done to the crack-closing property of the partially prestressed concrete beams, and the crack closing stress value is studied emphatically through whole courses analysis. (2) The uniform formula to crack closing moment is presented, which is fit well to the existed test data all. (3) The author’s research indicates that the calculational crack closing moment accord well with the measure one to disposition and unbounded partially prestressed concrete beams, when crack closing stress respectively equal to 1N/mm2 and 2N/mm2,. So crack closing stress can be take as 1N/mm2 and 2N/mm2 when calculate crack closing moment of partially prestressed concrete beams. (4) Introduce the main influencing factors and the calculating method ofthe crack width, and expatiate the virtue of crack controlling using nominal tensile stress. (5) The effect of the transverse crack width on the durability of partially prestressed concrete beams is studied, through analyzing the mechanic of reinforced corrrosio and previous exposed test. (6) The condition of crack closing is studied and combining with the load condition the concept of the unload coefficient is given, base on which, the application range of crack closing property to the partially prestressed concrete beams is given. (7) In the end, the proposal design formulas of crack controlling in the partially prestressed concrete beams is given, considering the crack-closing property and nominal tensile stress method.The design of a engineering example proved that a good economy benefit can be gained using the crack-closing property to crack controlling design of the partially prestressed concrete beams. And the prepositional formula can make a good use of the crack closing property to crack controlling design of the partially prestressed concrete beams. The prepositional formula has the conveniency of application, and clear concept, can be provided as a reference to the engineering designers and revise the code for design of concrete structures.更多还原